Image reproducer



Patented May 11, 1943 IMAGE REPRODUCER George A. Morton, Haddon Heights, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application September 28, 1940, Serial No. 358,752

3 Claims.

This invention relates to image reproducing systems and more particularly to those systems adapted to reproduce infra-red images.

The average human eye is not sensitive to infra-red or light rays whose wave lengths are greater than 7500 Angstrom units. In order that an infra-red image may be seen by the human eye, it is necessary to provide some auxiliary means for transforming the infra-red image into an image of light havi g wave lengths shorter than 7500 Angstrom uni It has been proposed to focus an infra-red image on a mosaic of electron-emissive elements and to scan the mosaic with an electron beam at a predetermined frequency in order to produce a train of picture signals which may be reproduced in the cathode ray tube whose scanning frequency is synchronized with the scanning frequency of the electron beam scanning the mosaic upon which has been focused the infra-red image.

It is well known that the band of wave lengths of light to which a photoelectric element is sensitive includes a range beyond that which a human eye is sensitive. However, beyond that range in the infra-red direction, the sensitivity of the photoelectric element drops off rapidly and only by very careful observations an infra-red light having a wave length of approximately 17000 Angstrom units may be detected and beyond this range in the longer wave length direction the photoelectric element is insensitive to infra-red rays.

According to this invention, an electrode comprising a sheet of heat insulating material with a metalized surface is covered with an extremely thin organic film. An infra-red image is then focused on the metalized surface. The heat from the image evaporates each element of area of film to a depth in accordance with the detail of the infra-red image so that when the metalized electrode is scanned by an electron beam a train of picture signals representing the infra-red image is produced. These signals are then transmitted to a picture tube where they are connected to an image of light whose wave length is within the range of sensitivity of the human eye.

The principal object of this invention is to provide a method and means for converting an infra-red image to an image perceptible to the human eye.

Another object of this invention is to provide a picture transmitter tube sensitive to infra-red rays.

A still further object of this invention is to contransmit infra red rays.

vert a heat image into a light image perceptible to the human eye.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which Figure 1 is a block diagram showing one form of this invention,

Figure 2 is an enlarged portion of a cross section of a heat sensitive electrode of the picture transmitting tube, v

Figure 3 is an enlarged portion of a cross section of another form of a heat sensitive electrode of the transmitter tube, c

Figure & is an enlarged portion of a cross section of a heat element of the transmitter tube showing the effect of an electron beam on the coating of the heat-sensitive electrode,

Figure 5 is another cross section of a portion of a heat sensitive element of the transmitter tube showing the function of the electron beam under different operating conditions,

Figure 6 is an enlarged portion of the cross section of the heat sensitive electrode showing the contact of the electron beam with a dark portion of the image,

Figure 7 shows an enlarged portion of the cross section of said heat sensitive electrode showing the contact of the electron beam with a "light portion of the image, and

Figure 8 shows another sensitive transmitter tube.

Referring to Fig. 1, a transmitter tube l contains an electron gun including a cathode 3, a control electrode 5, a first anode 1 and a second anode 9 to produce an electron beam ill. The elements of the electron gun are supplied with the necessary operating potential through resistance H connected to a direct current voltage supply source. An infra-red image I3 is focused on electrode l5 through an optical system including a lens I! and a window IS. The window I9 of the transmitter tube I is of a material adapted to Many materials of this rock salt, Sylvine (KCl) form of an infra-red type are known, such as or fluorite.

The electron beam I0 is caused to horizontally scan the surface of the electrode I5 by the cur rent in the horizontal deflecting coils 2| supplied by the horizontal deflection voltage wave generator 22. The vertical deflection is controlled by the current in vertical deflecting coils 23 supplied by the vertical deflection voltage wave generator 24. A suitable collecting electrode 25 is positioned adjacent the electrode I5 and maintained at a positive potential with respect to electrode H9 in order to collect secondary electrons which have been driven from electrode I5 by the impact of the electron beam in.

Turning now to Fig. 2, the electrode IE will be more fully described. A supporting member 21 is preferably of a material of low heat capacity, such as thin mica or Celluloid, upon which has been sprayed or condensed a layer 29 of metal or other conducting material of extreme thinness. This layer may be treated to increase its heat absorption (e. g.. by blackening). An organic material 3|, such as paraffin, is distilled until it consists of only molecules with, for example, 12 or 13 carbons, which forms thereon another extremely thin layer over the metal layer 29. Parafiins of different kinds may be used, such as may be found among the paraiiin and other petroleum derivatives.

When the infra-red image is focused upon the organic surface 3|, the heat of the image causes high and low irregularities in the surface. such as high place a and low place b, depending upon the dark" and light areas of the infra red image, respectively.

The thin organic coating 3| is evaporated under the impact of the electron beam, but the thin layer is continually replenished by a heated filament or other heater 26 which has thereon a heavy coating of the organic material. A filamerit. inside the cathode is supplied with current through source 28 and resistance 39. When the temperature of the cathode 26 is increased, the organic material is evaporated therefrom to condense on the electrode I5, thereby maintaining a thin layer of the organic material on the electrode I5.

Fig. 4 shows a greatly enlarged portion of the electrode I5 under a dark portion of the infra red image. The supporting member 21 having the metallized coating 29 and the organic coating 3| is scanned by the electron beam I9 so that the organic substance 3I is evaporated from the surface 29, as represented by the falling off portion of the organic substance in under the influence of the electron beam shown in greatly enlarged dimensions and moving in the direction from right to left. This is representative of the action resulting from the electron beam I9 striking a dark area of the electrode such as is marked a in Fig. 2.

Fig. 5 illustrates the results obtained when the electron beam I9 strikes a light area of the infra red image such as that represented by the thinner portion of the organic coating b in Fig. 2. The supporting member 2'! and its metallized layer 29 contains thereon the extremely thin layer of the organic material 3!. When the electron beam I strikes this organic substance, it is quickly evaporated so that a portion of the electron beam I9 strikes the metallized surface 29 to liberate secondary electrons, which are, in turn, collected by the collector element 25 of the transmitter tube I.

It will be understood that, under these conditions, there will be a different amount of secondary electrons driven from the electrode I5, the amount depending upon the intensity of the infra red ray on the electrode I under the point scanned by the electron beam II). It therefore follows that a train of picture signals representative of the infra red image may be obtained by scanning the electrode I5.

The train of picture signals taken from the metallized coating 28 (Fig. 1) of the electrode aaiaios i5 is led. to an amplifier it through the coupling condenser and resistor M. The amplified signal is then applied to the control electrode 99 of picture tube M through coupling condenser 43 and resistor 45. An electron beam ill is produced by the electron gun composed of the cathode 49, the first anode 5| and the second anode 53 to fall upon the luminescent screen 95. The intensity of the electron beam is governed by the potential on the control electrode 99 which receives its train of picture signals from the amplifier 34. The electron beam M is caused to scan the luminescent screen 55 in synchronism with the electron beam II] of the picture tube I by the excitation in the horizontal defleeting coils 51 supplied from the horizontal deflection voltage wave generator 22, which also supplies the horizontal deflecting coil H of the transmitter tube I. The vertical deflection of the electron beam 41 in tube 55 is caused by the excitation of coils 59 by the vertical deflection voltage wave generator 24, which also excites the vertical deflecting coils 29 of the picture transmitting tube I. The infra red images focused upon the electrode I5 of the transmitter tube I will therefore be reproduced on luminescent screen in the picture tube M as a visible light image.

Fig. 3 illustrates another form of the transmitting tube electrode I5 which contains a metallized coating 29 on the opposite side of the supporting member N as the organic coating 9|. The results obtained by the use of such an electrode are similar to those obtained by the use of an electrode of the type shown in Fig. 2, but the operation is slightly difierent. In the case of the electrode shown in Fig. 3, the impact of the electron beam on the "dark area a produces a certain capacitive effect on the metallized surface 29. When the electron beam strikes a light portion 12, there is less separation between the beam I0 and the surface 29 so that the capacitive efiect of the beam ill on the metallized surface 29 is changed, causing a picture signal to be produced as the beam I9 scans the irregular surface of the organic substance 3i, under the influence of an infra-red image.

The potential and current of the electron beam, upon striking the electrode I5, governs the rapidity at which the point of organic substance 3! at the beam point is evaporated. This potential may be controlled by the adjustment of resistance H controlling the positive potentials impressed upon the electron gun in the transmitter tube I. The current may be controlled by the control element 5.

Fig. 6 indicates the operation of the system wherein the electron beam has a high enough potential to completely evaporate the wax-like substance at the point of contact even if the area of the infra red image being scanned be dark. It will be noted that the organic material 3| is completely evaporated by the time the complete electron beam I9 has passed over it. If the electron beam I9 has a potential to cause the organic substance PM to completely evaporate such as shown in Fig. 6, the picture signals will result from the change in secondary emission from the metallized surface 29. It will be seen that the lighter areas of the infra-red image will cause more of the area of the metallized surface 29 to be subjected to the electron beam I9 because the heat of the lighter areas of the infra-red image has evaporated some of the wax-like film 3| so that when the beam 20 reaches the "light area, the wax-like film 3| is thinner.

If the potential of the electron beam at the point where it intercepts the electrode I5 (Fig. 7) of the transmitter tube I is reduced, the organic substance 3| will not be completely evaporated by the time the electron beam l has passed over it at any point, regardless of the intensity of the infra-red image. The resulting train of picture signals will be similar to those produced by the operation of the transmitter tube i under the condition shown in Fig. 6, but the theory of operation will again be slightly different. If the electron beam l0 does not come in contact with the metallized surface 29, there will be no secondary emission of electrons from the metallized surface. There will, however, be a change in capacitive effect because of the difference in thickness of the organic surface 3| between the electron beam I0 and the metallized surface 29 resulting from the infra red image which has previously changed the thickness of the wax-like material 3| in accordance with the brilliance of the image.

Fig. 8 illustrates another form of picture tube 63 and another form of equipment for focusing the image on the sensitive electrode I is shown. The picture tube 63 contains an electron gun and deflecting coils similar to that shown and described for transmitter tube I in Fig. 1. The window l9 which, as previously described, is adapted to transmit infra red rays, is positioned on the opposite side of the electrode 15 to that of the electron gun. The collector electrode 25 is positioned on the same side of the electrode l5 as the electron gun, but it is preferable that the cathode 26, adapted to replenish the surface of the electrode I5 with the thin organic layer 3|, be positioned on the same side of the electrode l5 as that side from which the infra red image is applied to the electrode l5.

The infra red image I3 is focused upon the electrode l5 by a concave mirror 65 or by the optical system disclosed by Stroemgren in Vierteljahrschrist, vol. 70, pages 65-86, in which a connecting plate is positioned in front of a reflector. In the case of the transmitter tube 63, wherein the image is focused upon the electrode IS on the opposite side of the electron gun, the electrode l5 preferably takes a form such as shown and described in more detail under Fig. 3, wherein the metallized surface 29 is on the opposite side of the supporting member 21 from the organic coating 3|. This allows the metallized surface 29 to come in contact with the electron beam.

The operation of the system under these conditions depends upon the change in capacitive effect resulting when the electron beam scans the irregular surface of the organic substance 3| under the influence of an infra-red image l3. This may be further explained by the fact that, under the conditions of a dark area a, there is more separation between the point of the electron beam and the metallized surface 29 than there would be when scanning a light area b. It follows, then, that a train of picture signals can be taken from metallized surface 29 of the electrode [5 of the transmitter tube 63 shown in,

Fig. 8, amplified, and reproduced on a luminescent screen such as shown by in tube ll of Fig. 1.

While several systems for carrying this invention into effect have been shown and described, it will be apparent to one skilled in the art that this invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of this invention as set forth in the appended claims.

I claim as my invention:

1. In combination, an envelope containing an electrode and having a window to pass infra red rays to said electrode, means for generating an organic vapor in said envelope to deposit on said electrode a coating whose thickness depends upon the intensity of said infra red rays, and means in said envelope for producing an electron beam to scan said electrode to produce a train of signals representative of the intensity of said rays.

2. In a system for converting infra red images to visible light images, an electron beam tube containing an electrode coated with a volatile coating, a window in said tube to pass infra red rays, means for focussing said infra red images upon said electrode to cause a base relief of said image in said coating, means for causing said beam to scan said electrode to produce a train of signals representative of the intensity of said images and to volatilize said coating, and means to replenish'said coating.

3. The method of converting infra red images into a train of signals representative thereof, comprising the steps of continuously coating an electrode with a volatile material, focusing said images on said electrode to volatilize said material in accordance with the intensity of said image, and scanning the electrode with an electron beam.

GEORGE A. MORTON. 

